System of control for electric motors.



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TBATEEITEB APR 14, 1908.

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SYSTEM GP GUNTRUIS POE ELEGTRIU MUTUESB mrmcmwm FILED FEB. a, 1906.

UNITED STATES PATENT OFFICE.

LEONARD A. TIRRILL, OF LYNN, MASSACHUSETTS, ASSIGNOR. TO GENERALELECTRIC COM- PANY, A CORPORATION OF NEW YORK.

SYSTEM OF CONTROL FOR ELECTRIC MOTORS.

To all whom it may concern:

Be it known that I, LEONARD A. TIRRILL, a citizen of the United States,residing at Lynn, county of Essex, State of Massachusetts, have inventedcertain new and useful Improvements in Systems of Control for ElectricMotors, of which the following is a specification.

The present invention relates to control systems for electric motors andmore particularly to motors which are adapted to be reversed fre uentlyand quickly under load. Such a con ition arises upon operating a planeror other machine having reciprocating parts, by means of an electricmotor, and securing the reversal of the reciprocating part by reversingthe direction of rotation of the motor armature. This service isobviously very severe upon the motor, since the reversal occurs withgreat frequency and must be effected in a short space of time and whileovercoming the momentum and inertia not only of the motor. itself, butof the load which isIbeing moved; and for this reason great difficultyhas been experienced in operating planers and similar apparatus by meansof reversing motors. It is further de sirable to make the motor run "ata higher rate of speed in one direction than in 'the other; for example,a slower speed is necessary on the cutting stroke of a planer than onthe return stroke.

The object of the invention is to provide a simple system whereby amotor is enabled to be reversed under the mostfavorable conditionspossible in service wherein the motor is required to be reversedfrequently while carrying a'material load; and to enable'the motor tooperate most advantageously at different speeds for different directionsof rotation.

To the above ends I employ a compound- 'wound motor, the shunt fieldwinding of which need not be opened during the process of reversing, andconnect the series field winding to the source of current supplyat thesame time that the motor armature is disconnected preparatoryto-reversing In this way a powerful field is built up while the armatureis being reversed. Adjustment of speed on the principal working stroke,such as the cutting stroke of a planer, may be made by varying thecurrent in the shunt field winding in the ordinary manner; and,

Specification of Letters Patent.

Application filed February 8, 1906. Serial No. 300,069.

adapted to be operated latented April 14, 1908.

.for producing faster operation in one direction than in the other, theinfluence of the shunt winding is eliminated so that the return speed isunaffected by adjustment of' the cutting speed. The'method ofcontrolling the shunt field for the purpose of increaslng the speed onthe return stroke consists preferably in opening a short-circuit about aresistance permanently in the shunt field circuit and having such avalue that when the short-circuit is opened the current in the shuntwinding is weakened to such an extent that the excitation roducedthereby is small as compared to t e total excitation. Thus the shuntwinding is practically eliminated without at any time opening itscircuit and without endangering the insulation of the shunt winding aswould be the case if its circuit were interrupted before every returnstroke, and the speed of the return stroke is determined by the strengthof the series field which of course may be made anything desired byproperly proportioning the series turnsi For a fuller explanation of thepresent invention and of its objects and advantages reference is tohadto the following description.

In. the accom anying drawing, Figure 1 shows a'motorr-iven planer adated to be controlled in accordance with t e present invention; Fig. 2 isa diagram showing a motor and one form of control ap aratus whereby thepresent invention may be carried out and Figs. 3 to 12 are diagramsshowing the motor connections during complete cyc es of reversals of themotor.

In the drawing the invention is illustrated as applied to a motor-drivenplaner but it is of course understood that the invention is not limitedto this articular use.

A indicates the p aner having the reciprocating member B, and M is amotor adapted to operate the same; C is a controller supported adjacentto or u on the planer and by adjustable stops 1) and b on thereciprocating member. These stops alternately enga c with an arm 0 onthe controller to operate t e same to reverse the motor; the distancebetween the stops determining the stroke of the reciprocating member.The controller may be either a main controller or a master controlleradapted to govern a motor controller. Since the present invention is notlimited to any particular type of controller, the sim ler form hasbeen-chosen for the purpose oi illustration.

In the diagram, Fig. 2, the motor consists of an armature 1, a seriesfield winding 2, and a shunt field winding 3; 4 is a resistance adaptedto be connected in series with the armature in starting the motor and tobe subsequently cut out; 5 is a rheostat in series with the shunt fieldfor the purpose of varying the speed at which the motor shall beoperated in one direction.

6 is a bank of resistances having a high resistance value and beinadapted, when connected in circuit with t e shunt windin to reduce thecurrent flow through the siunt winding to such an extent that the effectof the shunt winding becomes unimportant in comparison with the totalexcitation; L and L indicate aisource of current supply. The variousparts are so arranged that when the controller is in one extreme runningposition, namely, when the fixed contacts engage with the movablecontacts along line 1, 1, the motor rotates in a direction to move theplaten B of the planer through its cutting stroke. This is the positionwhich the controller assumes when the platen has been moved to theextreme left and the stop I) has come into en agement with the handle 0on the contro ler and moved it into one extreme positlon.

Assuming that the controller is in the running position corresponding tothe cutting stroke, circuits ma be traced as follows: from line L,throug rheostat 5, shunt field windin 3, contacts 8, 18, 17, and 7 ofthe control er, to line L. A second circuit extends from' line L,through controller contacts, 9, 19, 20, 10, through the armature of themotor, through controller contacts 11, 21, 23, 14, through the seriesfield winding, and thence through controller contacts 15, 24, 25 and 16,to line L Thus the armature and series winding are connected across theline with no external resistance in circuit and the shunt field windingis connected across the line in series'with rheostat 5; the resistance 6being short-circuited by the controller as shown in Fig. 3. The motor ispreferably so designed that a considerable variation in speed may beobtained by adjusting the rheostat 5, so that the cutting speed may bevaried to suit the requirements of any particular piece of work. The controller remains in this running position until the laner has nearlycompleted its cutting stro e, whereupon the stop 1) comes intoengagement with the arm c and begins to rotate the controller. The partsare so proportioned that the time required to shift the controller fromone extreme position to the other is sufficient to ermit the motor tobring itself and the p aten to rest, so that or operation as both thestop I) and the arm 0 are brou ht to rest at the same time and thecontroller is left in its sixth position, namely, the position forreturning t e platen preparatory to the next cutting stroke. It will beseen that in the second position or the first intermediate position ofthe controller, the current, after passing through the armature, insteadof flowing directly from contact 11 to contact 14, now passes fromcontact 11 through contacts 21 and 26, thence through resistance 4, andto contact 14 by way of contacts 13', 27, and 28. This condition isindicated in Fig.4. In the third osition, the armature is cut outentirely anr current flows from line L, through contacts 9, 19, 29 and12, through resistance 4, and thence through contacts 13, 27, 28 and 14,through the series field winding and thence through contacts 15, 24, 25and 16 to line L as shown in Fig. 5. Therefore, although the armature iscut out, full field is maintained, so that when in the fourth positionthe armature is again connected in, but in reverse relation to seriesfield (see Fig. 6), the field excitation is at its maximum, therebyproviding a maximum torque at the moment of reversal. If desired, thearmature when cut out may be short-circuited through a resistance in thethird position, thereby providing a dynamic braking action. In position5 the resistance 4 is again out out as indicated in Fig. 7. In the finalposition, the conditions are unchanged except that the short-circuitabout .resistance 6 is opened at contacts 7 and 8 as shown in Fig. 8, sothat the excitation due to the shunt winding is practically eliminated,and the platen is moved on its return stroke at a speed determined bythe speed of the motor acting as a series motor. It will be noted thatthis elimination of the shunt winding is effected without opening thecir- -cuit and therefore without endangering the insulation of themotor. Upon a )proaching the-end of its return stroke, the platen againreverses the controller and the motor is radually reversed and againconnected up i a compound-wound motor through the progressive stepsindicated in Figs. 9 and 12, and then the starting resistance 4 is againout out as indicated in Fig.3. It will now be seen that the presentinvention provides a simple method, and one readily carried out bysimple control apparatus, for controlling a reversing motor in certainclasses of service in such a manner that the most efficient results areobtained with the least strain on the motor and the ap aratus o )eratedthereby.

hatl ciaim as new and desire to secure by Letters Patent of the UnitedStates, is

1. The method of operating a compoundwound motor, which consists inrunning the motor on full field, reversing the connections of the motorarmature while on full field, and

. ing

motor.

then decreasing the excitation produced by the shunt field winding andrunning the motor as a series motor. 2. The method of o crating areciprocatmg motor-driven mem er adapted to move at different speeds inthe several directions of its travel,'which consists in connecting themotor for o eration as a compound-wound motor on in]? field, reversingthe connections of the armature while on full field, and then decreasingthe excitation produced by the shunt field winding and running the motorasaseriesmotonfl I 3. The method of operating a compoundwound motor,which consists in supplying current to the armature and field windin scutting out thearmature and connecting t e series field winding to thesource of current supply, connectin the armature in reverse re ation tothe series field Winding, and decreasing the excitation produced by theshunt winding to a'small proportion of its I whole value.

4. The method of operatinga compoundwound motor, which consists in su pling current to the armature and field windin s, cuttin out the armatureand connecting t e series eld winding to the source of current supply,connecting the armature in reverse re ation to the series field winding,andthen inserting a high resistance in series with the shuntfieldwinding.

5. The methodof o erating a reciprocatmotor-driven mem lver adapted tomove at different speeds in the several directions of its travels, whichconsists in connectin the operatin motor as a compound Wound motorand tien reversing the relative connections of the armature and series; fieldwindings and operating the motor as a series 6. The method of o crating,areciprocating motor-driven mem er adapted to move at different speedsin the several directions of its travel, which consists in connectingthe motor for operation as a" compound-wound motor, cutting out thearmature and connecting the series field winding to the source ofcurrent su ply, connecting thearmature reversely wit relation to thefield winding,

and then decreasing the excitation produced by the shunt field n- 7. Ina system of motor control, a com-- pound-wound motor ,and motorcontrolap paratus constructed and arran ed to connect the severalwindings of sai motor to a source of current supply for operation in onedirection, to reverse the motor onrfull field and to weaken the shuntfield excitation to a small roportion of the series field excitation.

8. n a system-of motor control, a com-- pound-wound motor and controlapparatus constructed and arranged to connect the out the armature andconnect the series field winding to the source of, current supply, to,connect the armature in reverse relation to the series winding, and toweaken the shunt field excitation to a small proportion of the seriesfield excitation. f

9. In a system of motor control, a comound-wound motor, a resistance intheshunt eldcircuit-arranged to weaken the shunt field excitation to asmall proportion of the series field excitation, and a controllerconstructed and arranged to short-circuit said resistance and connectsaid motor to ,a source of current supply for one direction of rotation,to reverse the motor on full field and then to open the short-circuitabout said resistance,

10; In a system of motor-control, a comin 1pound-wound motor, aresistance in the shunt eld circuit arranged to weaken the shunt 'fieldexcitation to a. small proportion of the series field excitation, and acontroller con structed and arranged to short-circuit said resistanceand connect the motor to a source of current supply for rotation in'onedirection, to cut out the armature and connect the series field windingto the source of current supply, to connect the armature in reverserelationto the series field windin and then to open the short-circuitabout said reto connect said motor to a source of current supply foroperation in one direction, to automatically reverse saidmotor on fullfield and to weaken the shunt field excitation to a small proportion ofthe series field excitation for operationin the reverse direction.

12. In combination, a reciprocating member adapted to travel faster inone direction than in the other, acompound-wound motor for driving saidreciprocating member, a resistance in the shunt field circuit adapted toweaken the shunt field excitation to a small roportion of its wholevalue, and a controlor constructed and arranged to short-circuit saidresistance and connect the motor to a source of current supgly forrotatlon in one direction, to reverse t e motor and then to open theshort-circuit about said resistance for operation in the reversedirection. I In witness whereof I have hereunto set my hand this sixthday of February, 1906.

. LEONARD A. TIRRILL.

Witnesses:

JOHN A. MoMAN s, Jr., HENRY O. Wnsrnnnxnr.

